Field of the Invention
The present invention relates to an electrochromic apparatus, an optical filter, an imaging apparatus, a lens unit, a window member, and a method of driving an electrochromic apparatus.
Description of the Related Art
An electrochromic (EC) phenomenon is a phenomenon in which a material is colored or decolored through changes in its light absorption region induced by a reversible electrochemical reaction (oxidation reaction or reduction reaction) caused at the time of application of a voltage. An electrochemically coloring/decoloring element utilizing the EC phenomenon is referred to as “electrochromic (EC) element,” and is expected to find applications as a light control element configured to change an optical transmittance.
As the EC element, there have been known an inorganic EC element using a metal oxide such as WO3, and an organic EC element using an organic low-molecular compound such as a viologen, a conductive polymer, and the like. Of those elements, it has been known that the organic EC element, in which a low-molecular organic material is colored/decolored in a solution state, has advantages of a sufficient contrast ratio in a colored state, a high transmittance in a decolored state, and the like. In addition, it has been known that the organic EC element has an advantage in that its color state can be arbitrarily controlled by mixing a plurality of materials having different absorption wavelengths.
In order to use such an organic EC element in an optical filter, there is required a drive method for controlling the optical transmittance arbitrarily. Further, it is also required to prevent a significant change in absorption spectrum of light absorption in the element even at the time of a change in optical transmittance.
As the drive method for controlling the optical transmittance, in Japanese Patent Application Laid-Open No. H11-109423, there is disclosed a pulse width modulation (PWM) drive method involving applying, to an inorganic EC element, a voltage for causing an electrochemical reaction as a pulse and controlling a ratio of a duration of voltage application to one cycle of the pulse (duty ratio).
Further, in “Solar Energy Materials & Solar Cells” 2012, pp. 104 and 140 to 145, there is such a disclosure that an organic EC element formed of a single type of material is operated through PWM drive. The ratio of the duration of voltage application for causing the electrochemical reaction to one cycle of the pulse (duty ratio) is controlled in the same manner as in Japanese Patent Application Laid-Open No. H11-109423. Further, in particular, during a remaining duration of the one cycle of the pulse, the voltage application is paused and the element is put into an open circuit state, which produces an advantage in that the power consumption can be made smaller than that of the drive method of Japanese Patent Application Laid-Open No. H11-109423.
In Japanese Patent Application Laid-Open No. H11-109423 and “Solar Energy Materials & Solar Cells” 2012, pp. 104 and 140 to 145, there is no disclosure of drive in which a transient response of an effective voltage is taken into consideration.